People with celiac disease have adverse reactions to the proteins that are found in wheat, barley and rye, collectively called "gluten." However, not everyone with the genetic predisposition for this autoimmune condition gets it. Still, blood relatives are known to be at a substantially elevated risk -- even if they don't have symptoms of digestive problems -- so specialists emphasize the importance of being tested.
Genetics
Scientific understanding of the genetic basis for celiac disease and other forms of gluten intolerance is still in its infancy. Inflammatory bowel disease specialist Dr. Dermot McGovern, writing in the March 2011 newsletter of the American Gastroenterological Association, made that point with a famous quote of Winston Churchill's: "Now this is not the end. It is not even the beginning of the end. But it is, perhaps, the end of the beginning." Past and ongoing multi-national studies including the Human Genome Project, the HapMap Project and genome-wide association studies, or GWAS, have been responsible for "truly astonishing" progress in recent years, McGovern wrote, but much remains to be learned.
Types
Celiac disease affects about 1 percent of the population. At least one of two genetic markers, called haplotypes, are present in all people with celiac disease. Most people with celiac disease have both. Still, even though about a third of the American population has those markers, the vast majority will never develop celiac disease. Scientists don't know how and why the genes get switched on, but they expect refinements in genetic research to shed light on this question. When they know, they can develop tests to predict which people in this at-risk group are most likely to develop the disease. An estimated 10 percent of the population has problems digesting gluten yet doesn't have the genetic signatures for celiac disease. Non-celiac gluten intolerance is the name given to this poorly understood spectrum of conditions.
Relatives At Risk
The Wm. K. Warren Medical Research Center for Celiac Disease in San Diego estimates that 15 percent of the first-degree relatives -- parents, siblings and children -- of people with celiac disease are at risk of having or developing it, as are about half that number of aunts, uncles and cousins. The disease can damage the small intestine even in people without symptoms, increasing the risk for various cancers and other serious health conditions. For that reason, celiac disease specialists urge all relatives of patients to be tested. If tests are positive, patients should be monitored, so treatment can begin as soon as possible if the disease becomes active.
Tests
Genetic screening is most useful for elimination purposes: people who don't have the haplotypes can't have celiac disease. However, when the genes are present and activated by foods containing gluten, the immune system releases characteristic antibodies that show up on blood tests. The Warren Center advises physicians that for a variety of reasons, blood tests may yield both false positive and false negative readings, so repeating or changing the types of tests is recommended if results are at odds with clinical suspicions. Finally, a biopsy of tissue from the small intestine will always reveal damage if a patient has celiac disease.
References
- National Digestive Diseases Information Clearinghouse: Celiac Disease
- Wm. K. Warren Medical Research Center for Celiac Disease: FAQ for Physicians
- University of Chicago Celiac Disease Center: Genetic Testing
- Science Daily; Science News; "Identification of Genetic Risk Factor for Celiac Disease Promises Improved Treatment"; June 12, 2007
- Expert Glossary: Haplotype Definition
- American Gastroenterological Association; "Recent Advances in the Genetics of IBD"; Dermot McGovern; March 2011
